In medical practice, the introduction of drugs or instruments into a patient sometimes involves a device known as a dilator sheath assembly. The dilator and sheath each resemble a tube, where the dilator fits into the sheath, and where a narrow distal tip of the dilator (dilator tip) helps to introduce the wider sheath into the patient.
In some embodiments, the combination of dilator and sheath includes a transition region, where the generally narrower dilator transitions to the somewhat wider sheath. Where a dilator sheath assembly is inserted into a patient, the force of insertion can result in damage to the sheath, where damage occurs at the point of transition. The damaged medical instrument, in turn, can cause trauma to the patient, during continued insertion or during removal of the sheath from the patient. In other words, trauma can occur to tissue where insertion of the dilator-sheath assembly results in deformation (damage) of the sheath tip, where continued attempts to insert or withdraw the damaged sheath can traumatize the tissue.
During insertion into the body of a 2-part medical device assembly such as: sheath/dilator; trocar/dilator; sheath or catheter and needle; the transition from the primary insertion device (dilator or needle) to the secondary device (sheath, trocar, or catheter) creates a potential for resistance to insertion. No matter how small the radius or acute the lead angle of the distal tip of the sheath, catheter, or trocar, the transition can result in resistance and snagging as it progresses through the tissue and vessel wall.
Furthermore, attempts to improve insertion by making the distal taper of the sheath thinner have led to buckling or deforming of the sheath tip during insertion. Techniques for measuring sheath buckling or kinking are available (see, e.g., Monga, et al. (2004) Systematic evaluation of ureteral access sheaths. Urology. 63:834-836). The bumped dilator of the present disclosure functions through pre-dilation of the tissue and vessel wall so that the transition at the distal sheath tip encounters less resistance upon insertion. Those skilled in the art readily understand that “dilator” as defined by “bumped dilator” in this application is coextensive with any leading distal edge of an emplacement apparatus known or later developed.
General details of the structure and methods of use of dilator sheath are as follows. A dilator is often used to aid in the insertion of the sheath. Dilators have a long tubular section, the outside diameter of which may be slightly smaller than the inside diameter of the sheath, where the smaller diameter allows the dilator to be inserted without undue friction, and to be pulled back out of the sheath.
Alternatively, body of dilator can have outside diameter that is greater than inside diameter of body of sheath (in non-assembled state), where in the assembled state, the body of the dilator and the body of the sheath are held elastically in continuous contact with each other (but where friction is not sufficient to prevent longitudinal movements of the dilator within the sheath). Dilators also may have a pointed tip on the distal end and a hollow longitudinal passageway running the entire length thereof. In practice, a dilator is inserted into the patient's body through the sheath and along the guide wire, where the guide wire allows the distal tip to extend into the incision hole in the patient's tissues, carefully enlarging the hole. The dilator is then removed along the guide wire prior to insertion of a catheter along the guide wire and into the sheath.
Dilators comprise a dilator tip located at the distal end of the dilator. The dilator tip can be described with reference to the longitudinal tubular body of the dilator, that is, to the region of the dilator occupying the greatest surface area and volume of the dilator. Typically, the longitudinal body of a dilator is parallel or non-tapered, and having a constant diameter. The dilator tip can consist of a tapered distal tip (see, e.g., U.S. Pat. No. 5,885,217 issued to Gisselberg and Hicks, U.S. Pat. No. 7,422,571 issued to Schweikert and Nardeo, and US 2009/0105652 of Beal and King). Each of the above patent documents is hereby incorporated by reference. The proximal portion of the dilator can also be conformed to increase in radius, not by way of a taper, but by way of an annular region that is perpendicular (90 degree angle) to the longitudinal body of the dilator (see, e.g., U.S. Pat. No. 5,499,975 issued Cope and Arnett). Moreover, the proximal portion of a dilator tip can increase in radius by way of an overhang or ratchet-shape, as shown, for example, in U.S. Pat. No. 5,292,311 issued to Cope. These patents are hereby incorporated by reference in their entirety.
Following insertion of the dilator-sheath assembly and removal of the dilator, the sheath body forms a conduit for inserting a catheter or other medical articles, as known to artisans.
Methods for inserting a catheter or sheath into a blood vessel involve the use of the Seldinger technique, which includes the initial step of inserting a needle into a patient's blood vessel. A guide wire is inserted through the needle and into the vessel. The needle is removed, and a dilator and sheath combination are then inserted over the guide wire. The dilator and sheath combination is then inserted a short distance through the tissue into the vessel. The combination of the needle, dilator, and sheath, can be advanced over the guide wire into the blood vessel. After this combination has been advanced, the dilator is removed. The catheter is then inserted through the sheath into the vessel to a desired location. The Seldinger technique, and variations thereof, and devices used to perform this technique, are described in Seldinger (1953) Acta Radiologica 39:368-376; U.S. Pat. No. 7,722,567 issued to Tal, U.S. Pat. No. 7,972,307 issued to Kraus, et al, and U.S. Pat. No. 7,938,806 issued to Fisher, et al, which are incorporated by reference. U.S. Pat. No. 6,004,301 issued to Carter, incorporated by reference in its entirety, provides several elementary diagrams that disclose the insertion of a needle through the patient's flesh, with insertion into a blood vessel. Trauma, insult, and injury, are often issues that require management and longer hospital time. Likewise, preventing trauma, insult, or injury, is important for these devices.
After the incision hole is sufficiently enlarged, the dilator is removed, leaving the sheath and guide wire in position inserted into the incision hole. The catheter is then inserted into the sheath, through the incision hole and into the blood vessel, and the sheath is then removed from around the exterior of the catheter. The disclosure also contemplates embodiments comprising a solid dilator, that is, a dilator that does not comprise a lumen, as well as trocars, catheter-sheath devices, and other devices that access body lumens.
When removing the sheath, and where a catheter or other device needs to remain within the sheath and needs to remain within the blood vessel, removal of the sheath is made possible by using a splittable sheath, sometimes called peelable or “tearaway.”
The following concerns the situation where the dilator-sheath assembly has been inserted into patient's blood vessel or other cavity, where the dilator has been withdrawn, and the dilator has been replaced with a catheter or other instrument. The sheath that can be split away from the catheter as the sheath is being removed from the patient. By splitting the sheath along its longitudinal axis as the sheath is being removed from the patient, the practitioner can pull out the sheath in such a way that the sheath can be removed without interfering with any hubs, luer fittings, clamps, cuffs, accessories assembled to the catheter (U.S. Pat. No. 7,938,806 issued to Fisher, et al.). Removal of the sheath, with use of either peelaway sheath or non-peelaway sheath, where residence of catheter remains in a blood vessel, has the advantage of eliminating any obstruction of blood flow through the vessel, that is, obstruction caused by the presence of the sheath.
Where a sheath includes a hub, the hub serves as a handle (wings; tabs), and as a mating point for the insertion and locking of the dilator device. When the sheath needs to be split apart to be successfully withdrawn from the patient's body while leaving the catheter in place, the hub will also have to be split apart in order to clear the catheter. Sheath splitting is necessary, for example, where the catheter has any encumbrance, such as a hub on its proximal end (see, e.g., U.S. Pat. No. 7,422,571 issued to Schweikert and Nardeo, which is incorporated herein by reference).
After the dilator is removed, and before the catheter is inserted through the sheath, the sheath becomes an open conduit, allowing blood to spurt from the vessel through the sheath or allowing air to be aspirated into the vessel through the sheath, neither of which is desirable or permissible. The practitioner conventionally has had to place a thumb or finger over the proximal opening of the sheath to prevent blood loss and air embolism; however, this restricts the practitioner's hand movement, and is not a reliable method. Alternatively, the device can include a valve for preventing blood loss and air emboli. For example, a valve can be configured to automatically close and seal the opening as soon as the dilator is removed.